The commission heard recently from two authors of a 2003 report saying densely packed fuel pools create a heightened danger of fire and a catastrophic release of radioactivity. They urged fuel older than five years be stored in dry concrete casks.

A third author of the report was Allison Macfarlane, then a researcher at the Massachusetts Institute of Technology and now chairwoman of the NRC.

A Vermont Yankee spokesman says about 85 percent of the waste in the plant's spent fuel is more than 5 years old.

The Nuclear Energy Institute, an industry group, says it believes the risks are small.